Background:

Toll-like receptors (TLR) are a family of pathogen-associated molecular pattern recognition receptors expressed by cells of the immune system. TLR7 and TLR9 are expressed in endosomal compartments of human B cells and plasmacytoid dendritic cells (pDCs) and recognize molecular patterns of nucleic acids. There is growing evidence that immune complexes containing nucleic acids induce proinflammatory cytokines through TLR7 and TLR9 and exacerbate certain autoimmune diseases. Women are more prone to manifestation of autoimmune diseases than men. This study was carried out to evaluate the differences in immune responses induced through TLR7 and TLR9 in peripheral blood mononuclear cells (PBMCs) and plasmacytoid dendritic cells (pDCs) of healthy female and male subjects.

Methods:

We measured cytokine induction and costimulatory marker upregulation in response to specific TLR agonists in PBMCs and pDCs obtained from healthy male (n=15, age: 2360 years) and female (n=15, age: 1858 years) subjects. The agonists used in these studies include an RNA-based TLR7 agonist and a DNA-based TLR9 agonist. To further discern differences in TLR7- and TLR9-mediated immune responses in systemic lupus erythematosis (SLE) patients (n=9, age: 2978 years) on treatment with plaquenil/hydroxychloroquine and healthy female subjects (n=10, age: 2256 years), we measured cytokine induction in PBMCs in response to TLR7 and TLR9 agonists.

Results:

In PBMCs from healthy females, TLR7 agonist induced higher levels of IFN-a, and IP-10 and lower levels of IL-1Ra, IL-1b, IL-6, IL-8 and IL-10 compared with PBMCs from healthy males. The levels of IL-12, MIP-1b, and MCP-1 induced by TLR7 agonist were not different in PBMCs from females and males. pDCs from females showed higher levels of TLR7 agonist-induced IL-12, IP-10, IFN-a, and TNF-a than pDCs from males. TLR9 agonist induced similar levels of immune responses in PBMCs and pDCs from females and males, except IL-1Ra levels were higher in PBMCs from males than females. In studies comparing SLE patients with healthy female controls, TLR7 agonist induced lower levels of IFN-a, TNF-a, IP-10, and IL-6 in PBMCs from SLE patients than healthy females. TLR9 agonist induced lower levels of TNF-a, IL-6, MIP-1a, and MIP-1b in PBMCs from SLE patients than PBMCs from healthy females. The lower levels of TLR7- and TLR9-mediated immune responses in PBMCs from SLE patients could be a result of treatment with plaquenil, an inhibitor of endosomal TLR-mediated immune responses through neutralization of endosomal acidification.

Conclusions:

Notable differences in TLR7-mediated immune responses were observed in PBMCs and pDCs from healthy females compared with males that may play a role in autoimmune diseases afflicting females disproportionately.